The present invention relates to a control device of an engine which is provided with an exhaust gas recirculation device, and more particularly, to the control device of the engine for preventing occurrence of low speed pre-ignition which occurs, while the engine is operated at low speed rotation and a high load.
In many cases, an engine which is mounted on a vehicle or the like is provided with an exhaust gas recirculation device. The exhaust gas recirculation device recirculates a part of an exhaust gas which is exhausted from a combustion chamber of the engine to the atmosphere through an exhaust passage, into an intake passage, thereby to lower combustion temperature inside the combustion chamber, and to restrain exhaustion of nitrogen oxide (NOx) which is contained in the exhaust gas.
Moreover, there has been a technique for reducing abnormal combustion inside the combustion chamber of the engine, using the exhaust gas which is recirculated to the intake passage (hereinafter referred to as “recirculated gas”) by the exhaust gas recirculation device.
For example, in JP-A-S62-131961, an exhaust port of the recirculated gas to the intake passage is disposed near the combustion chamber, and a direction of the exhaust port is so set that the recirculated gas which is introduced into the combustion chamber flows along an inner peripheral wall of a cylinder. The recirculated gas which is swirled along the inner peripheral wall of the cylinder inside the combustion chamber forms an annular layer of the recirculated gas in a region near the inner peripheral wall. As the results, in a center part of the combustion chamber where an ignition plug is disposed, concentration of the exhaust gas is relatively lowered thereby to enhance ignition performance, while in an outer peripheral part of the combustion chamber, the concentration of the exhaust gas near the inner peripheral wall of the cylinder is enhanced thereby to restrain a phenomenon of self ignition of an end gas, that is, so-called knocking.
Moreover, in JP-A-2010-84619, there is disclosed a technique for predicting a self ignition phenomenon which is called as low speed pre-ignition. A cause for occurrence of ordinary pre-ignition is, for example, a deposit which is accumulated inside the combustion chamber. After this deposit is peeled off from a wall face of the cylinder, the deposit is exposed to burning, and red heated, resulting in a source of the self ignition. On the other hand, a cause for occurrence of the low speed pre-ignition besides the above described deposit is considered to be drops of lubricating oil which are splashed, for example, from the inner peripheral wall of the cylinder. The drops of the lubricating oil are fired with a rise of the temperature inside the combustion chamber, and become a fire source for the self ignition of a gas mixture.
As measures for preventing the ordinary pre-ignition, there is a method of delaying an ignition time. On the other hand, as measures for preventing the low speed pre-ignition, there is a method of lowering temperature of an intake air, and a method of lowering concentration of oxygen in the gas mixture, for example. However, in case where the method of lowering the temperature of the intake air is adopted, remarkable reduction of output power is incurred, depending on condition of operation, in some cases. Moreover, in case where an amount of the recirculated gas which is introduced into the intake air is increased for the purpose of lowering the concentration of oxygen in the gas mixture, for example, in Patent Document 1, the pre-ignition is induced to the contrary, in some cases. For this reason, there is a limit in increasing the amount of the recirculated gas.